linux-kernel - Re: [announce] "kill the Big Kernel Lock (BKL)" tree

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Message-ID: <alpine.LNX.1.10.0805151041380.16151@fbirervta.pbzchgretzou.qr>
Date:	Thu, 15 May 2008 10:44:57 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Jonathan Corbet <corbet@....net>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Alexander Viro <viro@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [announce] "kill the Big Kernel Lock (BKL)" tree 


On Wednesday 2008-05-14 23:45, Jonathan Corbet wrote:
>Sez Ingo:
>1: We could add an unlocked_open() to the file_operations structure;
>   drivers could be converted over as they are verified not to need the
>   BKL on open.  Disadvantages are that it grows this structure for a
>   relatively rare case - most open() calls already don't need the BKL.
>   But it's a relatively easy path without flag days.

1b: add a .locked_open and move all BKL-requiring code to use that.
When time comes and BKL is gone, .locked_open can be removed again,
and no rename was ever done for BKL-free code.

>2: Create a char_dev_ops structure for char devs and use it instead of
>   file_operations.  I vaguely remember seeing Al mutter about that a
>   while back.  Quite a while back.  This mirrors what was done with
>   block devices, and makes some sense - there's a lot of stuff in
>   struct file_operations which is not really applicable to char devs.
>   Then struct char_dev_ops could have open() and locked_open(), with
>   the latter destined for removal sometime around 2015 or so.

Iff you create a new char_dev_ops, don't clutter it with the old stuff.
BKL-using code could continue using file_operations, would not it?

>3: Provide a new form of cdev_add() which lets the driver indicate
>   that the BKL is not needed on open (or anything else?).  At a

This is the BSD/Solaris tactic, heh :)

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